Bottle Py: Enabling CORS for jQuery AJAX requests

Question

I'm working on a RESTful API of a web service on the Bottle Web Framework and want to access the resources with jQuery AJAX calls.

Using a REST client, the resource interfaces work as intended and properly handle GET, POST, ... requests. But when sending a jQuery AJAX POST request, the resulting OPTIONS preflight request is simply denied as '405: Method not allowed'.

I tried to enable CORS on the Bottle server - as described here: http://bottlepy.org/docs/dev/recipes.html#using-the-hooks-plugin But the after_request hook is never called for the OPTIONS request.

Here is an excerpt of my server:

from bottle import Bottle, run, request, response
import simplejson as json

app = Bottle()

@app.hook('after_request')
def enable_cors():
    print "after_request hook"
    response.headers['Access-Control-Allow-Origin'] = '*'
    response.headers['Access-Control-Allow-Methods'] = 'GET, POST, PUT, OPTIONS'
    response.headers['Access-Control-Allow-Headers'] = 'Origin, Accept, Content-Type, X-Requested-With, X-CSRF-Token'

@app.post('/cors')
def lvambience():
    response.headers['Content-Type'] = 'application/json'
    return "[1]"

[...]

The jQuery AJAX call:

$.ajax({
    type: "POST",
    url: "http://192.168.169.9:8080/cors",
    data: JSON.stringify( data ),
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function(data){
        alert(data);
    },
    failure: function(err) {
        alert(err);
    }
});

The server only logs a 405 error:

192.168.169.3 - - [23/Jun/2013 17:10:53] "OPTIONS /cors HTTP/1.1" 405 741

$.post does work, but not being able to send PUT requests would defeat the purpose of a RESTful service. So how can I allow the OPTIONS preflight request to be handled?

Answer 1

Install a handler instead of a hook.

There are two complementary ways I've done this in the past: decorator, or Bottle plugin. I'll show you both and you can decide whether one (or both) of them suit your needs. In both cases, the general idea is: a handler intercepts the response before it's sent back to the client, inserts the CORS headers, and then proceeds to return the response.

Method 1: Install Per-route (Decorator)

This method is preferable when you only want to run the handler on some of your routes. Just decorate each route that you want it to execute on. Here's an example:

import bottle
from bottle import response

# the decorator
def enable_cors(fn):
    def _enable_cors(*args, **kwargs):
        # set CORS headers
        response.headers['Access-Control-Allow-Origin'] = '*'
        response.headers['Access-Control-Allow-Methods'] = 'GET, POST, PUT, OPTIONS'
        response.headers['Access-Control-Allow-Headers'] = 'Origin, Accept, Content-Type, X-Requested-With, X-CSRF-Token'

        if bottle.request.method != 'OPTIONS':
            # actual request; reply with the actual response
            return fn(*args, **kwargs)

    return _enable_cors


app = bottle.app()

@app.route('/cors', method=['OPTIONS', 'GET'])
@enable_cors
def lvambience():
    response.headers['Content-type'] = 'application/json'
    return '[1]'

app.run(port=8001)

Method 2: Install Globally (Bottle Plugin)

This method is preferable if you want the handler to execute on all or most of your routes. You'll just define a Bottle plugin once, and Bottle will automatically call it for you on every route; no need to specify a decorator on each one. (Note that you can use a route's skip parameter to avoid this handler on a per-route basis.) Here's an example that corresponds to the one above:

import bottle
from bottle import response

class EnableCors(object):
    name = 'enable_cors'
    api = 2

    def apply(self, fn, context):
        def _enable_cors(*args, **kwargs):
            # set CORS headers
            response.headers['Access-Control-Allow-Origin'] = '*'
            response.headers['Access-Control-Allow-Methods'] = 'GET, POST, PUT, OPTIONS'
            response.headers['Access-Control-Allow-Headers'] = 'Origin, Accept, Content-Type, X-Requested-With, X-CSRF-Token'

            if bottle.request.method != 'OPTIONS':
                # actual request; reply with the actual response
                return fn(*args, **kwargs)

        return _enable_cors


app = bottle.app()

@app.route('/cors', method=['OPTIONS', 'GET'])
def lvambience():
    response.headers['Content-type'] = 'application/json'
    return '[1]'

app.install(EnableCors())

app.run(port=8001)

Answer 2

Here's a minor improvement on @ron.rothman's method #2 for installing the CORS handler globally. His method requires you to specify that the OPTIONS method is accepted on every route you declare. This solution installs a global handler for all OPTIONS requests.

@bottle.route('/<:re:.*>', method='OPTIONS')
def enable_cors_generic_route():
    """
    This route takes priority over all others. So any request with an OPTIONS
    method will be handled by this function.

    See: https://github.com/bottlepy/bottle/issues/402

    NOTE: This means we won't 404 any invalid path that is an OPTIONS request.
    """
    add_cors_headers()

@bottle.hook('after_request')
def enable_cors_after_request_hook():
    """
    This executes after every route. We use it to attach CORS headers when
    applicable.
    """
    add_cors_headers()

def add_cors_headers():
    if SOME_CONDITION:  # You don't have to gate this
        bottle.response.headers['Access-Control-Allow-Origin'] = '*'
        bottle.response.headers['Access-Control-Allow-Methods'] = \
            'GET, POST, PUT, OPTIONS'
        bottle.response.headers['Access-Control-Allow-Headers'] = \
            'Origin, Accept, Content-Type, X-Requested-With, X-CSRF-Token'

```

Answer 3

Also shouldn't you actually be using this?

response.set_header('Access-Control-Allow-Origin', '*')
response.add_header('Access-Control-Allow-Methods', 'GET, POST, PUT, OPTIONS')

Answer 4

Consider letting your webserver, not Bottle, set the headers.

Not sure whether this applies in your situation, but I've solved the problem in past projects by setting CORS headers for my Bottle application in Apache. It's easy to configure, keeps my Python code nice and clean, and is efficient.

Information is available from many sources, but if you're using Apache, here's what my config looks like (more or less):

<Location "/cors">
    Header set Access-Control-Allow-Headers "Origin, Content-Type"
    Header set Access-Control-Allow-Methods "POST, GET, OPTIONS"
    Header set Access-Control-Allow-Origin "*"
    Header set Access-Control-Request-Headers "Origin, Content-Type"
</Location>